Perhaps this fits in the FAOW or Mofo threads but at this point it deviates a bit.
I am playing with some more flea-power ideas and was selecting a front end to add some gain to my mini-mofo.
And in the spirit of throwing stuff to the wall and seeing what sticks, I got the idea that perhaps we can replace the mofo biasing network and the input cap with a JBOZ style input stage. You can see what I came up with in the attachments below.
We basically have a JBOZ kind of input with its mid-point set at the biasing V for the output mosfet (4.5ish V). By removing the coupling caps, we bias the mosfet. But at the same time we significantly limit the undistorted output because the midpoint is set asymmetrically very low. Gain and biasing is configured by changing R6 which makes everything a function of the PSU V.
In the attachment, with 0.15V input the amp is already starting to clip. Green is Vin, blue is Vout, red is power at the load and cyan is power at the mosfet
The J113 is running at around 15mA and 100mW max with a 20x gain, while the IRF510 is biased at around 450mA and starts clipping at just below 3V p2p (18ish W peak), which is ~1W of output (0,5ish W RMS)
With a 12V PSU, the gain was 8x at 7ish W peak on the mosfet.
One thing to note, is that the positive swing probably has to be limited with a couple of leds or something, in case someone forgets that this is a 1W amp and fries the mosfet because of the larger headroom on the positive side. Of course we could limit the PSU too (we probably won't)
Also, biasing is sensitive to R6 changes, so it probably has to be split to a resistor plus a trimmer for better control.
Can you please review my idea?
I am playing with some more flea-power ideas and was selecting a front end to add some gain to my mini-mofo.
And in the spirit of throwing stuff to the wall and seeing what sticks, I got the idea that perhaps we can replace the mofo biasing network and the input cap with a JBOZ style input stage. You can see what I came up with in the attachments below.
We basically have a JBOZ kind of input with its mid-point set at the biasing V for the output mosfet (4.5ish V). By removing the coupling caps, we bias the mosfet. But at the same time we significantly limit the undistorted output because the midpoint is set asymmetrically very low. Gain and biasing is configured by changing R6 which makes everything a function of the PSU V.
In the attachment, with 0.15V input the amp is already starting to clip. Green is Vin, blue is Vout, red is power at the load and cyan is power at the mosfet
The J113 is running at around 15mA and 100mW max with a 20x gain, while the IRF510 is biased at around 450mA and starts clipping at just below 3V p2p (18ish W peak), which is ~1W of output (0,5ish W RMS)
With a 12V PSU, the gain was 8x at 7ish W peak on the mosfet.
One thing to note, is that the positive swing probably has to be limited with a couple of leds or something, in case someone forgets that this is a 1W amp and fries the mosfet because of the larger headroom on the positive side. Of course we could limit the PSU too (we probably won't)
Also, biasing is sensitive to R6 changes, so it probably has to be split to a resistor plus a trimmer for better control.
Can you please review my idea?
